/Engine/Source/Runtime/Engine/Classes/GameFramework/PlayerController.h
also GameModeBase::GetSeamlessTravelActorList() (the function that's called on servers)
virtual void GetSeamlessTravelActorList ( bool bToEntry, [TArray](API\Runtime\Core\Containers\TArray)< class [AActor](API\Runtime\Engine\GameFramework\AActor) * > & ActorList )